This proposal is for the development of a prototype single photon computed tomography (SPECT) scintillation camera for the detection and functional imaging of breast tumors using radioactive tracers. The camera will have a stationary annular crystal detector, to surround a pendant breast in close proximity and image it three-dimensionally, in its entirety, independent of radiotracer concentrations in other body organs. The construction of this camera is made possible by unique scintillation camera innovations, developed during phase I of this project, which modify the way that light is directed and received by the camera s photomultipliers. The annular camera is expected to provide the highest possible sensitivity, resolution and tumor contrast that can be achieved by scintigraphic means. These improvements should result in higher specificity and detection of tumors than is possible by any other means. PROPOSED COMMERCIAL APPLICATION Because of its higher specificity and detectability, annular SPECT of an isolated breast has the potential of being used in conjunction with or replacing existing diagnostic methods in many instances.